Enforcing the law and providing emergency assistance often require emergency vehicles to park in a lane or on the shoulder of a road or highway.

To increase safety, Ontario's Highway Traffic Act requires motorists when approaching a police, fire or ambulance vehicle stopped with its red lights* flashing in the same direction of travel, either in aane or on the shoulder of the road to slow down and pass with caution. If the road has two or more lanes, the motorist must move over into another lane, if it can be done safely.

* Fire vehicles and ambulances use flashing red lights. Police vehicles may use flashing red lights or a combination of flashing blue and red lights.